The highly toxic G-type nerve agents, which include sarin (GB), soman (GD), and cyclosarin (GF) are considered weapons of mass destruction. Upon inhalation or dermal penetration, they attack the nervous system by interfering the degradation of neurotransmitter acetylcholine leading to death. Permanent damage to the nervous system can also occur at non-lethal doses. Immediate application of antidotes to an affected person could prevent permanent damage. However, exposure to low levels of nerve agent leads to ambiguous signs and symptoms that cannot be easily discriminated from other conditions. The inability to detect nerve agents at low-concentration may result in a delay in treatment and permanent damage.
Extensive efforts have been made to develop sensors for sarin and similar compounds, however, detection below ppb level remains a difficulty. To overcome this limitation, pre-concentration techniques are frequently used to detect target molecules from the air. However, pre-concentration techniques have their own challenges, particularly in the field, including that they can be time consuming.
Chemical gradients in hydrogel films have been reported to concentrate model analytes, such as charged dye molecules, at least 40-fold by biasing diffusion such that the dye is directionally transported to a central point in the film at a rate of few micromeres per minute. While the concept of gradient-directed transport is attractive because it enhances the sensor response, the slow transport velocity limits the applicability for real time detection. This also assumes an appropriate read-out mechanism exists for the concentrated analyte.
Existing techniques to not adequately address the need for a simple field solution to detect trace levels of chemical agents. Accordingly, a better solution for the selective and rapid detection of chemical agents at very low concentrations is needed.